1. Field of the Disclosure
The present disclosure relates to a multiple light projection type image display apparatus that combines lights from a plurality of light sources and projects a resulting light, and a control apparatus therefor.
2. Description of the Related Art
As a projection type image display apparatus (hereinafter described also simply as a “projector”), there are a liquid crystal projector that projects images by making light penetrate a liquid crystal display device, and a DLP (Digital Light Processing) (registered trademark of Texas Instruments Incorporated) that projects images by reflecting light on a reflection type mirror device such as a DMD (Digital Micro-mirror Device).
As white light sources used for these projectors, there are used discharge lamps of high intensities such as a high pressure mercury lamp, a xenon lamp, and a metal halide lamp.
When a discharge lamp is driven by a direct current power source, the lifetime of the lamp is disadvantageously shortened since the temperature of the anode becomes higher than that of the cathode due to collision of electrons with the anode at the time of arc discharge.
Therefore, it is beneficial to drive the anode and the cathode in a cyclical switchover manner by applying an alternating current of a predetermined frequency to the electrode pair.
Moreover, in order to achieve high brightness, a multiple light type projector that projects light combined from a plurality of light sources has been generally known (See a Patent Document 1 of Japanese patent laid-open publication No. JP 2009-204646 A).
Since the light sources 211 and 221 of the Patent Document 1 are stepped down by a down converter 91, the operating frequencies of the switching devices become the same as each other.
Accordingly, for example, it is assumed that the operating frequency of the power source is 100 kHz±5%, the peak value of the unnecessary radiation level of the light source 211 is 21 dB, and the peak value of the unnecessary radiation level of the light sources 221 is 20 dB.
Then, the unnecessary radiation characteristic 28 of a total of unnecessary radiation characteristic 26 of the light source 211 and the unnecessary radiation characteristic 27 of the light source 221 are added up in an overlapped manner in the vicinity of the frequency of 100 kHz±5%, and therefore, the peak value of the unnecessary radiation level as a multiple light projector becomes 41 dB of the total of peak values of the unnecessary radiation levels of the light source 211 and the light source 221.
That is, the peak value of the unnecessary radiation level as the multiple light projector disadvantageously becomes a value that exceeds the peak value of the unnecessary radiation level of the individual light sources.